As a 12-nation hunt for a missing Malaysia Airlines plane spread out Saturday across the Indian Ocean and reached over land toward Kazakhstan in Central Asia, some experts raised the incredible possibility that a 250-ton Boeing 777 might never be found.

“If that triple seven flew for four hours, and you look at that four-hour radius, you could spend a lifetime looking and not even cover a fraction of the area you are searching,” said John Fish, vice president of American Underwater Search and Survey, who has been involved in multiple ocean searches for missing aircraft. “But if they can get more information from the navigational system and other satellites, they could narrow the search.”

And if the plane is located and its black boxes retrieved, 40 years of airline accident investigation techniques suggest that the mystery of Flight 370 might be solved in a matter of hours.

Malaysia Airlines Flight 370, carrying 239 people, disappeared from air traffic control radar at about 1:30 a.m. March 8 as it neared the southern coast of Vietnam en route to Beijing.

The transponder, which identifies the plane to air traffic controllers, stopped functioning. The pilots made no distress calls, and data transmissions from onboard computers and radar blips suggest that the pilots or an intruder deliberately diverted the plane from its flight path and then flew a zigzag course for multiple hours.

Black Boxes

Aviation crash mysteries often end once the cockpit voice recorder and flight data recorder, known commonly as the "black boxes," are mined for the information stored inside. The twin units, which are actually bright orange in color and built to withstand fire and a high-speed crash, are stowed in the aircraft’s tail section, where they are least likely to suffer damage.

The world may never learn what happened at the crucial moment when the plane was diverted from its flight path because the cockpit voice recorder, which operates in a continuous loop during flight, captures only two hours of conversations between the pilots, along with their radio calls to air traffic controllers.

Usually, that's more than enough for an accident investigation.

If the pilots of the Malaysian plane or an intruder spoke in the cockpit toward the end of the flight, their voices will be on the recorder. But if the plane did indeed fly on for multiple hours, whatever confrontation took place that precipitated the disaster will be lost.

Data Recorders

That doesn’t mean investigators would be at a dead end to sort out a criminal motive.

The National Transportation Safety Board (NTSB) concluded that the copilot of an Air Egypt jet that crashed off New York in 1999, killing all 216 people on board, had committed suicide. The copilot was heard on the cockpit voice recorder saying “I rely on God” seven times. It was a good clue, but not conclusive evidence.

The flight data recorder revealed that the operation of the flight controls indicated a struggle in the cockpit and a deliberate effort to shut down the engines and crash the plane.

The flight data recorder has become such a sophisticated instrument that its information often solves the case very quickly. It captures more than 1,000 characteristics of nearly every instrument on board, from the engines to lavatory smoke detectors.

The recorder collects data on airspeed and altitude as well as information on flight controls that would reveal if they are operating properly.

In 1996, when an Aeroperu flight crashed off the coast of South America, killing all 70 people on board, the flight data recorder revealed that the plane’s static ports—which convey the plane’s altitude and airspeed data to the cockpit—were not working properly.

The plane had been washed the night before the flight and the ports had been taped over by the maintenance crew, who failed to remove the tape afterward. To confirm the findings, investigators retrieved the piece of the plane that held the static ports but left the rest of the wreckage on the seafloor.

Crew members tow part of the wreckage from Air Bus A330-200, a jetliner that crashed in the Atlantic Ocean with 228 people on board in June 2008.

PHOTOGRAPH BY FORCA AEREA BRASILEIRA VIA LATINCONTENT/GETTY

If the Malaysian plane had been changing altitude erratically in steep rises and drops, as theWall Street Journal reported Friday, those movements will be collected on the flight data recorder.

Because the whole episode involving the Malaysian plane is unusual, one unknown factor to consider is how effectively whoever was controlling the plane was able to “hide” its activities. If the transponder and other identifying systems were deliberately turned off, could the black boxes also have been disabled? That is unclear.

But the investigation of a 1997 SilkAir flight that crashed in Sumatra, Indonesia, killing 104 people, suggests that scenario is possible. On the SilkAir flight, the cockpit voice recorder stopped working. Investigators suspected, but were unable to confirm, that the circuit breaker for the cockpit voice recorder had been pulled, disabling the device. The official Indonesian accident report never determined the official cause of the accident. But the NTSB concluded in its own report that the crash was the result of one pilot’s suicide.

Clues in the Wreckage

The black boxes don’t always tell the tale.

When the cargo door of a United Airlines plane blew off on a Honolulu-to-Sydney flight in 1989, the plane returned safely to Hawaii but the door lay on the ocean floor for months.

Without that door, the National Transportation Safety Board initially concluded that it had popped open because its lock had been damaged in a previous flight. Once the door was hauled up from the Pacific, investigators found that an electrical failure had forced it open.

“You can’t prove what happened until you’ve proved what didn’t happen,” said Michael Barr, who teaches aviation accident investigation at the University of Southern California.

Barr once investigated a cargo plane that crashed just after taking off from Sacramento, California. When the investigators first arrived to examine the wreckage, they assumed that the plane’s center of gravity had not been calculated, a common practice at the time. Neglecting to do that could upset the weight balance in a plane, causing it to stall on takeoff.

By the second day, they determined the plane held so little cargo that the center of gravity wasn’t relevant.

“They found out part of the tail fell off because the plane had just come out of maintenance, where someone didn’t put a nut on a bolt," he said. "Because of that, the horizontal stabilizer failed."

TWA Flight 800 crashed off the coast of Long Island, N.Y. in July 1996. Its wreckage was reconstructed in a hangar in Calverton, N.J.

PHOTOGRAPH BY ED BETZ, AP

Mock-ups and Reconstructions

But even if all of an aircraft’s pieces are recovered and examined, investigators sometimes find they still need to learn more from the plane. Then they reassemble the fuselage, a time-consuming task that's akin to putting together a jigsaw puzzle.

After the terrorist bombing of Pan Am Flight 103 over Lockerbie, Scotland, in 1988, British accident investigators reassembled the plane’s fuselage in a hangar, in what is still considered the best reconstruction ever conducted.

Their work revealed that the bomb blew a fairly small hole in the 747’s front cargo bay, which at first seemed puzzling. Then investigators learned that the shockwaves from the bomb peeled the aircraft’s skin off the frame, according to a former investigator who worked on the case.

As a result, the plane lost structural integrity and broke up.

Part of a China Airlines 747 fuselage was also reassembled when investigators were at first unable to resolve why the jumbo jet broke up in midair, killing all 225 people on board.

It turned out that a faulty repair to the plane’s tail had caused unseen deterioration for more than 20 years before finally giving way after the plane took off from Taipei in 2002. Investigators found tar on the outside of the fuselage, where cigarette smoke had seeped through tiny cracks.

The Unexpected Is Possible

Airline investigators are a conservative lot by nature and not inclined to chase after exotic theories. The catalogue of accidents over the past four decades falls into well-established patterns of possible causes. There are only so many things that can go wrong.

“If you look at all the aircraft that have disappeared over the past 40 years, there has never been a case of anyone turning off the electronics and sneaking away at lower altitudes," said Fish. "It would be unprecedented."

That doesn’t mean it couldn’t have happened.

FBI agents probing the crash of TWA Flight 800 off Long Island in 1996, killing 230 people, were convinced the 747 was bombed. Until they weren’t.

Tension between FBI agents working the accident and the NTSB has become part of the folklore around the crash. The FBI agents on the case became convinced a bomb explosion broke up the plane because bomb residue was found on the wreckage.

The NTSB investigators were dubious of that from the start because none of the wreckage carried the distinctive signature that a bomb explosion would make on metal. But they weren’t able to prove that the jet’s center fuel tank exploded until they first disproved a bomb was on board.

Finally, after a long search through aircraft records, investigators learned that the residue had been deliberately placed on the plane four weeks before the crash as part of a bomb-detection drill using bomb-sniffing dogs.

“No 747 ever went down because of a spark in the center fuel tank until TWA,” Barr said. “No 767 ever went down because an Egyptian pilot committed suicide. Because the triple seven has a pretty good safety record, this [Malaysian accident] has got to be something new—or a human factor.”

As the search became so impossibly large, Bloomberg News reported Saturday that the last satellite transmission from the plane showed it flew south toward western Australia and may be in the Indian Ocean off of Perth.

“The old search area in the Gulf of Thailand was like looking for an automobile in the state of Ohio,” said Fish. “The new search area would be like expanding that to include all the lower 48 states.”

But the clock is ticking. The pingers on the black boxes that identify their location will run out of battery life and fall silent in less than three weeks.